Physiology and Signals Flashcards
Dynamic nature of biosignals
1) (Quasi) static - e.g. the core body temperature would
be a (quasi) static biosignal,
exhibiting relatively slow
circadian changes over 24 h
2) Dynamic - e.g. the instantaneous beat-to-beat
changes of the heart rate
Origin of bioelectric signals
generated by muscle and
nerve cells, membrane potential source (Action potential), ECG, EMG, EEG, etc., most widely used, transducer is used to
convert ions flow to electrical signal
Origin of biomagnetic signals
Organs such asbrain, heart and lungs produce weak magnetic fields with
information not included in
bioelectric signals, low Signal-to-Noise (SNR) type signals
Origin of biomechanical signals
1) These are signals that
originate from a mechanical action of the biological system. Examples: Motion and displacement signals, pressure, tension, flow.
2) Some signals can be difficult to measure as
they don’t propagate, need to measure at the exact site using invasive methods
Origin of optic biosignals
1) benefit from light absorption
and scattering, which are related to propagation volume and medium, both
changing in a physiologically relevant way. An artificial light is used.
2) Optoplethysmogram
can be used to monitor e.g. cardiac function.
Bioacoustic signals
Many physiological
phenomena generate acoustic noise – flow of
blood in the heart, valve sounds, flow of air in
the airways, sounds in the digestive track, joint
sounds etc., measured on the surface of the body using accelerometers or microphones
Biochemical signals
signals that are a result
from a chemical analysis of blood or tissue in the lab. Examples: levels of oxygen PO2, or level of carbon dioxide PCO2.
General requirements for transducers
1) accuracy
2) stability - changes with properties in time should not be rapid
3) lack of interference - impossible to stop all
Challenges for biomedical signals
1) Signals are low amplitude (µV-mV) with artifacts presenting challenges for instrumentation design, amplification will introduce error and noise
2) Signals can be highly variable (complex) and can depend on the patient, properties, frequency content, variance
3) Signals can have several artefacts (couplings) and can be difficult to interpret
All living cells in the body, have an electrical potential across the cell membrane. Body fluids surrounding cells are conductive solutions containing charged atoms known as ions. What are excitable cells?
Components of nervous and muscular tissue that exhibit a resting potential and an action potential by passage of ions through a semi-permeable membrane. This process is necessary for information transfer (e.g. sensory info in nervous
system or coordination of blood pumping in the heart)
What causes resting potential?
1) concentration imbalance of ions
2) diffusion and electrical forces oppose each other - equilibrium/steady state reached
3) steady state PD is resting potential ~70 - 90mV relative to conductive ionic medium
4) cells in polarised state
Resting potential of excitable cells
1) corresponds to equilibrium potential, at equilibrium thermal forces balance other existing forces and fluxes in both directions are equal.
2) Bilipid layer of cells contain selective ion channels (transport specific ions)
3) conductivity/resistance to motion depends on voltage across channel
4) membrane analogous to capacitor, channels analogous to non-linear resistor/conductance (voltage-dependent), PD (battery) across membrane
5) non-linear behaviour of ion channels allow action potentials
What does the Nerst (Ek) potential represent?
1) potential difference corresponding to the situation where electrical energy balances the diffusional (chemical) energy for a specific ion
2) each ionic species has a different equilibrium potential
3) higher relative intracellular concentration of ions (e.g. K+, Cl-) = negative equilibrium potential. higher relative extracellular concentration (e.g. Na+, Ca2+)
Explain the process of
1) Ions pass through ion selective channels (only allow one type of ion to pass)
2) resistance to ion motion depends on potential difference across channel
3) Each
